netdev - [PATCH 1/3] skb: Drop bad code from pskb_expand

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Date:	Fri, 04 May 2012 17:26:46 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, eric.dumazet@...il.com,
	jeffrey.t.kirsher@...el.com
Subject: [PATCH 1/3] skb: Drop bad code from pskb_expand_head

The fast-path for pskb_expand_head contains a check where the size plus the
unaligned size of skb_shared_info is compared against the size of the data
buffer.  This code path has two issues.  First is the fact that after the
recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info
is always placed in the optimal spot for a buffer size making this check
unnecessary.  The second issue is the fact that the check doesn't take into
account the aligned size of shared info.  As a result the code burns cycles
doing a memcpy with nothing actually being shifted.

Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
---

 net/core/skbuff.c |   12 ------------
 1 files changed, 0 insertions(+), 12 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c199aa4..4d085d4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 		fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
 	}
 
-	if (fastpath && !skb->head_frag &&
-	    size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
-		memmove(skb->head + size, skb_shinfo(skb),
-			offsetof(struct skb_shared_info,
-				 frags[skb_shinfo(skb)->nr_frags]));
-		memmove(skb->head + nhead, skb->head,
-			skb_tail_pointer(skb) - skb->head);
-		off = nhead;
-		goto adjust_others;
-	}
-
 	data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
 		       gfp_mask);
 	if (!data)
@@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 
 	skb->head     = data;
 	skb->head_frag = 0;
-adjust_others:
 	skb->data    += off;
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 	skb->end      = size;

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